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Sears twin 18

3052 Views 21 Replies 7 Participants Last post by  searstractorfan
Hi guys i have a sears about 1979 or 80 twin 18 that i am wanting to make a puller out of. What are these engines RPM and how hard is it to get it up close
to 4000 RPM? Paul
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Are you going to pull at the West Branch tractor show in July?
Don't know for sure. I would have to check the dates. I have my own pulling club and track in Grayling. So usually on a sat. i am working on my track and we pull on Sun. I usually don't plan a pull on the weekend of the West Branch show because i camp out there and show some old tractors.
Do you pull there? Paul
They are governed to 3600 I believe. Honestly, I have never need more from my Onans, and the BG/MS that is in the SS18 is an absolute power house. I think you would be fine with 3600 but thats just me.
Well the last few pulls last year i tryed pulling with this sears twin 18. and i wanted to pull in 3 hi. i had 23x10.5x12 turf and some times i would run out of engine just a few feet short of a full pull. Now i bought some 12 inch wheels and a set of 24x12x12 tires. I was thinking about changing the engine pulley to slow the 3rd gear down but it would still be faster than 2nd . Can any body tell me how to figure out these gear ratios? I know the larger tires will make it faster so to slow it down for more power, how much smaller would the engine pulley have to be? I was running a 1050 and 1250 class. Paul
I run 26x12x12 tires, and run 2nd high..Ive NEVER gotten a motor to carry 3rd high yet...even my big N52M trys but wont...put a zip tie in the govenor spring to pull the RPMS up...that way you get the full 4000rpms.. RPMS is if you can hold the RPMS up, that means more speed you will can actually move as fast with slower speed gears as you can with bigger ones IF ur rpms are up...but change the pulleys to get the desired speed...
Thanks for you reply's What you are saying is what i was thinking. I come so close in 3rd hi, so if i get my rpm up and change engine pulley to slow 3rd hi down a little, that will still be a lot faster than 2nd hi. Another thing i am changing is, last fall i had wheel weights and this year i took them off and i am
going to melt down some lead and make my own weights to put on tractor and not the wheels. Paul
for him to pull high 3rd he'd have to go just a touch smaller on the engine pulley cuz hes running out of power now
your right the engine pulley would have to go smaller to slow the tractor down and keep power up. I have already made it faster with the tires being a little larger so now i will have to slow it down some with smaller pulley. I wonder if i could find a adjustable pulley like i use on my furnace blowers?
It will be easier this year because last year we run a 1050 and 1250 class.
This year i changed the weight class to 1050 and 1150. Paul
The new tires are 24 inches tall, and the old are 23 inches tall. Take 24 and divide it by 23 which gives you 1.04xxxxxxx. We'll round it to 1.04 so you get the idea here. Now take your engine pully size and divide it by 1.04, and that will give you the same speed as before. Let's say the pulley is 3 inches. 3 divded by 1.04 equals 2.88 inches. Chances are you won't find that size, so let's go to the driven pulley. Lets say it is 6 inches. (I have no clue what these machines run for pulleys, so bare with me.) Take 6 times 1.04 equals 6.24 inches. So the closest you're going to get for this value is 6.5 which is .26 inch difference. Now the other value of 2.88 inches, you can go down to 2.5 inches. A .33 inch difference. So it depends on how bad it was bogging down, If it was just barely bogging, I use the 6.5 as a driven pulley. If it was bogging a little more, then I would go with the 2.5 engine pulley. But the best way to figure this out would be to get the tire runout. The 23's should be roughly 72.22 inches of runout. And the 24's should be roughly 75.36 inches of runout. If this is too confusing, (Which I can understand that it can be.) Give us the engine pulley size, the driven pulley size, and find out what the runouts on the 23 and 24 inch tires are. Just take a tape measure and wrap it around the tire to see how many inches around it is. I'm sure we can figure it out for you.
No i did not understand all that. you are right on the OD of the tires as i recall about 72+ and about 75.5. What i don't understand is if there was a 6" pulley on the engine and you have already made the tractor faster by tire size ,then you would have to use smaller pulley on engine to slow it back down. If you make the engine bigger like a 6.5 then you are increasing speed??? Paul
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